This invention relates to a method for processing spent radioactive ion exchange resin formed in a nuclear power plant and particularly to a processing method whereby the volume of the waste resin is reduced while the waste resin is converted into stable inorganic compounds by thermal decomposition.
The operation of a nuclear power plant is accompanied with the formation of waste liquid containing a variety of radioactive substances, and these waste liquid are processed in most cases with ion exchange resin. The processing of spent resin produced thereby has been a problem of a nuclear power plant operation. For example, spent ion exchange resin accounts for a considerable portion of the radioactive wastes in a boiling water reactor power plant.
Heretofore, spent ion exchange resin is solidified in a drum by mixing it with a solidifying agent such as cement or asphalt, and stored and kept in the plant area. However, the volume of these radioactive wastes tends to increase year after year, so that the acquisition of their storage place and the security of safety during their storage have been important problems. Accordingly, a great concern has been paid about reducing the volume of spent waste resin as much as possible in solidifying it.
For example, processes for the volume reduction of radioactive waste ion exchange resin include those based on acid decomposition. One of them is a process called HEDL Process (Hanford Engineering Development Laboratory Process) comprising acid-decomposing the resin at a temperature of 150.degree. to 300.degree. C. by using concentrated sulfuric acid (about 97 wt. %) and nitric acid (about 60 wt. %). Another example is a process described in Japanese Patent Laid-Open No. 88500/1978, comprising acid-decomposing the resin by using concentrated sulfuric acid and hydrogen peroxide (about 30%). Although a high volume reduction ratio can be obtained in these acid decomposition processes because the resin is decomposed after dissolution and the decomposition solution is concentrated by evaporation, there are a number of difficult problems, such as handling of a strongly acidic solution, corrosion of equipment by a concentrated strongly acidic solution, and an unestablished technique of solidifying a recovered concentration solution.
Accordingly, Japanese Patent Laid-Open No. 1446/1982 proposed a process in which no strong acid is used and which comprises decomposing waste resin by using hydrogen peroxide in the presence of an iron catalyst. Since, however, this process requires a large quantity of hydrogen peroxide, there is a problem that the cost is high because of the expensiveness of hydrogen peroxide and, in addition, decomposition itself is not sufficient and organic matter remains undecomposed.
Still another process proposed in Japanese Patent Laid-Open No. 12400/1982 comprises burning waste resin by using a fluidized bed. However, this process has a problem that it generates a large quantity of exhaust gas which also must be subjected to appropriate disposal procedures.